JP3236032B2 - Liquid crystal display device and gradation driving method of the liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a gradation driving method for the liquid crystal display device, and more particularly to a gradation driving technique for an active matrix type liquid crystal display device. In recent years, TFT / LCD (Thin Film Transistor Liq
uid Crystal Display) is widely used as a pocket television of about several inches because a small, lightweight and high-quality display can be obtained. Recently, display panels with a screen size of about 10 inches have been manufactured as displays such as laptop personal computers and word processors, and those capable of displaying 512 colors in combination with an 8-gradation driver have been provided. . In such a gradation driver of a liquid crystal display device, it has been demanded that a small and low-cost operational amplifier having a small slew rate can be used.

[0002]

2. Description of the Related Art Conventionally, in an active matrix type liquid crystal display device, a technique of displaying 512 colors using an 8-gradation driver has been used. FIG. 6 is a diagram showing each liquid crystal cell in the liquid crystal display device, and FIG.
FIG. 3 is a diagram illustrating voltage characteristics.

As shown in FIG. 6, a liquid crystal cell LC has a TFT controlled by the level of a scan bus line SL.
, And is driven by a voltage between the data bus line DL and the common CM. The voltage levels (output levels of the liquid crystal driving power supply) V0 to V7 for driving each of the liquid crystal cells LC are set, for example, as shown in FIG.

FIG. 8 is a diagram showing switching of a voltage level at the time of line inversion of a liquid crystal display device. As described above, the liquid crystal display device (the liquid crystal cell LC) is driven at eight gradations by, for example, eight voltage levels V0 to V7. Here, in the active matrix type liquid crystal display device, the polarity of the level (voltage level V0 to V7) of the data bus line DL with respect to the common CM is inverted for each frame or each scanning line in order to prevent the characteristic deterioration of the liquid crystal. AC drive.

[0005]

FIG. 9 is a diagram for explaining inversion driving in a liquid crystal display device. by the way,
In the case of the frame inversion drive (see FIG. 9A),
When the liquid crystal display device is AC-driven by inverting the polarity for each frame, the output stage buffer of the liquid crystal drive power supply requires a slew rate (unit :) as long as the current capacity (> 100 mA) is sufficient to sufficiently charge and discharge the liquid crystal cell. V / μs) is not a problem. However, in the case of the line inversion drive (see FIG. 9B), that is, in the case of inverting the polarity for each scanning line to drive the liquid crystal display device with an alternating current, a large slew rate is required.

More specifically, as shown in Table 1 below, when the liquid crystal display device is AC-driven by inverting the polarity for each scanning line, the voltage level V0 is about 4 V for each scanning line.
At the voltage level V7, it is necessary to swing about 11V, so a large slew rate is required. Since a slew rate of about 2 V / .mu.s (change time of 5 .mu.s) or more is required, a large-size buffer (operational amplifier: operational amplifier) is required, and the price is high.

[0007]

[Table 1] The present invention has been made in view of the above-mentioned problems of the conventional liquid crystal display device, and has as its object to provide a liquid crystal display device having excellent display quality using a small and inexpensive buffer.

[0008]

According to the present invention, an n-stage voltage level for realizing an n-gradation display is set, and the polarity of the voltage level applied to the liquid crystal display panel is inverted to form the liquid crystal. A grayscale driving method for a liquid crystal display device for driving a display panel, wherein the n-stage voltage levels are set such that an even-numbered voltage level is set as one polarity with respect to a common level every other voltage level, and an odd-numbered voltage level is set. set the voltage level of the turn as polarity opposite to the polarity of the voltage level of a few number the even, and outputs a voltage level of said n stages from the output stage buffer corresponding, its absolute value odor
Te defines a pair of output <br/> Chikaradan buffer for outputting a pair of voltage levels that are adjacent to each other, at the time of polarity reversal, the output stage buffer for outputting a voltage applied to the liquid crystal display panel,
Switching between the specified pair of output stage buffers and switching between the specified pair of output stage buffers.
One output voltage is supplied to the other of the pair of output stage buffers.
The output voltage before polarity reversal is equal in absolute value.
A gray scale driving method characterized in that the voltage is converted to a higher voltage without changing the polarity before and after the polarity inversion .

[0009]

According to the gradation driving method of the liquid crystal display device of the present invention, the voltage levels of n stages for realizing the n gradation display are such that every other voltage level, even-numbered voltage levels correspond to the common level. One of the polarities is set, and the odd-numbered voltage level is set as the polarity opposite to the polarity of the even-numbered voltage level, and n-stage voltage levels are output from the corresponding output stage buffers. And in absolute value
A pair of output stage buffer that outputs a pair of voltage levels that are adjacent is defined, during polarity reversal, a pair of output stage buffer for outputting a voltage applied to the liquid crystal display panel is defined
Between the output stage buffers
One output voltage of the specified pair of output stage buffers is
Output of a pair of output stage buffers before the other polarity inversion
Before and after polarity reversal to a voltage equal in absolute value to the voltage
Is converted without changing the polarity . This makes it possible to provide a liquid crystal display device having excellent display quality using a small and inexpensive buffer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a liquid crystal display device according to the present invention and a gradation driving method of the liquid crystal display device will be described below with reference to the drawings. FIG. 1 is a diagram showing setting of voltage levels in a gradation driving method of a liquid crystal display device according to the present invention. In order to drive the liquid crystal display device using an 8-gradation driver, the voltage levels are set to V0 to V7. Shows the case. As shown in the figure, in the gradation driving method of the liquid crystal display device of the present embodiment, the voltage levels V0 to V7 are such that the even-numbered voltage levels V0, V2, V4, and V6 are on the positive voltage side with respect to the common level. And odd-numbered voltage levels V
1, V3, V5, and V7 are set to be on the negative voltage side. When the polarity is inverted, the polarity relationship between the voltage levels is reversed, and the display data is converted. Here, the voltage level V0 is included in the even number, but the numbering of this voltage level is V1
Needless to say, it may be set as V8.

Specifically, first, as shown in the following Table 2, a pair of adjacent voltage levels (V0, V1); (V2, V3); (V4,
V5); (V6, V7) are defined, and conversion is performed between the voltage levels of each pair. That is, when inverting from positive to negative, for example, the voltage level (selection voltage level) V0 is converted to V1, the voltage level V1 is converted to V0, the voltage level V2 is converted to V3, and V3 will be converted to V2. Thus, the polarity is different between the scan line N (positive polarity) and the scan line N + 1 (negative polarity) in FIG. 1 at the same voltage level. In the gradation driving method of the liquid crystal display device according to the present embodiment, the swing width of the voltage level is one voltage level (0.5 volt in FIG. 1), and the line is reduced by using a buffer (op-amp) having a small slew rate. Inversion driving becomes possible.

[0012]

[Table 2] Further, as shown in Table 3 below, conversion of display data is performed by inverting the least significant bit of the display data. That is, when inverting from the positive polarity to the negative polarity, for example, the display data 000 is converted to 001, the display data 001 is converted to 000, the display data 010 is converted to 011 and the display data 01 is converted to 011.
1 will be converted to 010.

[0013]

[Table 3] FIG. 2 is a block diagram showing a position embodiment of the liquid crystal display device according to the present invention. In the figure, reference numeral 1 is a personal computer (PC), 2 is a data conversion circuit, 3 is a timing generation circuit, 4 is a liquid crystal drive power supply, 5 and 6 are data drivers, 7 is a scan driver, and 8 is a liquid crystal display. The panel is shown.

Personal computer (host device) 1
Is a 3-bit digital R for each color for the data conversion circuit.
A GB signal (image signal) is supplied, and a horizontal and vertical synchronization signal (synchronization signal) is supplied to the timing generation circuit 3.
Supply. The data conversion circuit 2 receives the image signal from the personal computer 1 and outputs a display data signal to the data drivers 5 and 6, and receives the line inversion signal and converts the display data. Here, the conversion of the display data in the data conversion circuit 2 is performed according to, for example, Table 3 described above. That is, in the case of the positive polarity, the display data from the personal computer 1 is output as it is, and in the case of the negative polarity, the display data obtained by inverting the least significant bit of the display data is output.

The timing generation circuit 3 receives a synchronization signal from the personal computer 1 and outputs a data driver timing signal, a scan driver timing signal, and a line inversion signal. Here, the data driver timing signal is supplied to the data drivers 5 and 6, the scan driver timing signal is supplied to the scan driver 7, and the line inversion signal is supplied to the data conversion circuit 2 and the liquid crystal driving power supply 4. still,
The liquid crystal display panel 8 is an active matrix type liquid crystal display panel, and is driven by data drivers 5, 6 and a scanning driver 7.

FIG. 3 is a circuit diagram showing an example of a liquid crystal driving power supply in the liquid crystal display device of FIG. 2, and FIG. 4 is a diagram showing set voltages of the liquid crystal driving power supply of FIG. As shown in FIG. 3, the liquid crystal driving power supply includes a negative voltage level generator 11, a negative voltage level inverting unit (positive voltage level generator) 12, a voltage level switching unit 13, and an output stage buffer 14. . Here, the output stage buffer 14 includes the data drivers 5 and 6
16 buffers are provided in order to supply eight levels of voltages to the respective buffers.

As shown in FIGS. 3 and 4, the set voltages V0 to V0 of the liquid crystal driving power supply supplied to the data driver 5 are set.
V7 is set so that even-numbered voltage levels V0, V2, V4, and V6 are on the positive voltage side with respect to the common level, and odd-numbered voltage levels V1, V3, V5, and V7 are set on the negative voltage side. It is set to be. On the other hand, the set voltages V0 to V7 of the liquid crystal driving power supply supplied to the data driver 6
Is set so that the even-numbered voltage levels V0, V2, V4, and V6 are on the negative voltage side with respect to the common level.
The odd-numbered voltage levels V1, V3, V5, and V7 are set on the negative voltage side.

In the above description, each of the 16 buffers in the output stage buffer 14 is composed of an operational amplifier having a current capacity of about 100 mA and a slew rate of about 0.2 V / μs. That is, according to the liquid crystal display device of the present embodiment, since a small and inexpensive buffer (operational amplifier) can be used, a liquid crystal display device using a line inversion driving method with excellent display quality can be provided at a low price. can do.

FIG. 5 is a diagram showing an example of a line inversion signal in the liquid crystal display device of FIG. As shown in the figure, the liquid crystal display device of FIG. 2 outputs, for example, 525 horizontal synchronization signals in a vertical synchronization time of 16.7 ms, and outputs a line inversion signal corresponding to the horizontal synchronization signal. It has become. This example is for the 640 × 480 dot mode generally used in personal computers and the like.

[0020]

As described in detail above, according to the liquid crystal display device and the gradation driving method of the liquid crystal display device of the present invention,
An even-numbered voltage level is set as one polarity with respect to a common level at every other voltage level for every n voltage levels for realizing n-gradation display, and an odd-numbered voltage level is set to an even-numbered voltage level. polarity opposite to the voltage level of the set n steps as polarities output from the corresponding output stage buffer to define a pair of output stage buffer that outputs a pair of voltage levels that are adjacent to each other in the absolute value, the polarity At the time of inversion, an output stage buffer for outputting a voltage applied to the liquid crystal display panel is connected to a specified pair of output stage buffers.
With switching back and forth between the Ffa, defined pair
The output voltage of one of the output stage buffers is
The absolute value of the output voltage before the other
Change polarity before and after polarity reversal to equal voltage in value
By performing the conversion without using the buffer, a liquid crystal display device having excellent display quality can be provided using a small and inexpensive buffer.

[Brief description of the drawings]

FIG. 1 is a diagram showing setting of a voltage level in a gradation driving method of a liquid crystal display device according to the present invention.

FIG. 2 is a block diagram showing a position embodiment of the liquid crystal display device according to the present invention.

FIG. 3 is a circuit diagram showing an example of a liquid crystal driving power supply in the liquid crystal display device of FIG.

FIG. 4 is a diagram showing a set voltage of a liquid crystal driving power supply of FIG. 3;

FIG. 5 is a diagram showing an example of a line inversion signal in the liquid crystal display device of FIG.

FIG. 6 is a diagram showing each liquid crystal cell in the liquid crystal display device.

FIG. 7 is a diagram showing light transmittance-voltage characteristics of a liquid crystal.

FIG. 8 is a diagram showing voltage level switching at the time of line inversion of the liquid crystal display device.

FIG. 9 is a diagram for explaining inversion driving in the liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Personal computer 2 ... Data conversion circuit 3 ... Timing generation circuit 4 ... Liquid crystal drive power supply 5, 6 ... Data driver 7 ... Scan driver 8 ... Liquid crystal display panel

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/36 G02F 1/133 550 G02F 1/133 575 G09G 3/20 623

Claims (5)

(57) [Claims] 1. A liquid crystal display device for driving a liquid crystal display panel by driving the liquid crystal display panel by inverting the polarity of a voltage level applied to the liquid crystal display panel while setting n levels of voltage levels for realizing n gradation display. A driving method, wherein the n-stage voltage levels are set such that an even-numbered voltage level is set as one polarity with respect to a common level at every other voltage level, and an odd-numbered voltage level is set to the even-numbered voltage. A pair of output stage buffers which output a pair of voltage levels adjacent to each other in absolute value thereof. When the polarity is inverted , the output stage buffer for outputting the voltage applied to the liquid crystal display panel is connected to the specified pair of outputs.
With switching back and forth between the Chikaradan buffer, the defining
The output voltage of one of the pair of output stage buffers
Output of a pair of output stage buffers before the other polarity inversion
To a voltage equal in absolute value to the voltage before polarity reversal
A gradation driving method characterized in that conversion is performed later without changing the polarity . 2. The method according to claim 1, wherein the switching of the output buffer for outputting a voltage applied to the liquid crystal display panel is performed by converting display data between a pair of adjacent gradation levels. The gradation driving method for a liquid crystal display device according to claim 1, wherein 3. The gradation driving method according to claim 2 , wherein the conversion of the display data is performed by inverting the least significant bit of the display data. 4. The gradation driving method for a liquid crystal display device according to claim 1, wherein a line inversion driving method is applied to the liquid crystal display device. 5. A liquid crystal display device for driving a liquid crystal display panel by setting n levels of voltage levels for realizing an n gray scale display and inverting the polarity of a voltage level applied to the liquid crystal display panel. A timing generator circuit for receiving a synchronization signal from the host device and outputting a data driver timing signal, a scan driver timing signal, and a line inversion signal; and setting the n-level voltage levels to an even-numbered voltage level every other voltage level. Is set as one polarity with respect to the common level, and the odd-numbered voltage level is set as the polarity opposite to the polarity of the even-numbered voltage level, and the n-stage voltage levels are output from the corresponding output stage buffers. Output and adjacent to each other in absolute value
Output stage buffers for outputting a pair of voltage levels
Define, receiving said line inversion signal, the defined
The output voltage of one of the pair of output stage buffers is
Output voltage of the output stage buffer before the other polarity inversion
Voltage before and after polarity reversal
A liquid crystal drive power supply that converts without changing the characteristics , a scan driver that receives the scan driver timing signal to drive the liquid crystal display panel, and a data driver that receives the data driver timing signal and drives the liquid crystal display panel. A data conversion circuit that receives the image signal from the host device and outputs a display data signal to the data driver, and that receives the line inversion signal and converts the display data between a pair of adjacent grayscale levels. A liquid crystal display device comprising: